1. Field of the Invention
The invention relates to an epoxy resin composition including polyepoxides having at least two 1,2-epoxide groups which are obtainable by reaction of (i) di- or polyepoxides or mixtures thereof with monoepoxides, and (ii) one or more amines chosen from sterically hindered amines, disecondary diamines and diprimary diamines, subsequent reaction of the epoxide-amine adduct with polyfunctional isocyanates, and if appropriate, addition of further 1,2-epoxide compounds and curing agents. The epoxy resin compositions are useful as coatings for bridging cracks, as adhesives and as constituents of paints.
2. Description of Related Art
Epoxy resins, in particular those which are prepared from bisphenol A and epichlorohydrin, are known raw materials for preparing high-quality casting resins, coating compositions, and adhesives. These aromatic epoxy resins, when cured with polyamines, have good adhesive strength on many substrates, in addition to good resistance to chemicals and solvents. Bisphenol A epoxy resins which can be processed without solvents and are of the lowest possible viscosity are of considerable importance, inter alia, for the protection and restoration of concrete buildings. These epoxy resins can be cured using polyamines at ambient temperature. The usefulness of epoxy resins/polyamine systems, however, often is limited by an inadequate elasticity or flexibility in the cross-linked state. For permanent bridging of cracks, coating materials are required which "work" over the crack on the basis of their high elasticity and can withstand exposure to wide changes in temperature due to a high extensibility. Furthermore, elastic epoxy resin systems which still have an adequate elasticity at low temperatures (for example down to -20.degree. C.) are required in the adhesive sector.
In principle, the elasticity of epoxy resin systems can be increased externally by addition of plasticizers or internally by reduction in the cross-linking density. External elasticizing agents, however, are not reactive and are not incorporated into the thermosetting resin network. External plasticizers which can be employed are tar, phthalic acid esters, high-boiling alcohols, ketone resins, vinyl polymers and other products which do not react with epoxy resins and amine hardeners. However, this type of modification is limited only to specific fields of use since it has a number of disadvantages. Thus, these additions lead to a marked interference in the thermosetting resin structure, are limited in their plasticizing effect at low temperatures, tend to exudate when exposed to heat and during aging, and embrittle the cured systems.
To increase the elasticity internally, compounds that react with the epoxy resins or hardeners and that are co-incorporated in the cross-linking are added. Specifically, the elasticizing action is achieved by incorporation of long-chain aliphatic or highly branched additions into the resin or hardener component. These starting components should have the lowest possible viscosities, however, to enable processing of the resin-hardener systems without problems.
U.S. Pat. No. 3,538,039 discloses heat-curing mixtures of (1) an adduct of a polyepoxide and amine, (2) a polyfunctional anhydride and (3) an accelerator for the anhydride. The adduct preferably is built up from a polyepoxide and aromatic amines, such as aniline, m-aminophenol, m-phenylenediamine and methylenedianiline.
U.S. Pat. No. 3,518,220 discloses heat-curable epoxy resin mixtures of (1) an adduct, containing epoxide groups, of a polyepoxide having on average more than 1.0 vicinal epoxide groups and an aromatic amine having at least two active hydrogens on the nitrogen, and (2) 3-aminopyridine. Methylenedianiline, aniline, m-aminophenol, m-phenylenediamine and the like are used as amines.
DE-A 38 03 508 describes a cold-curing resin, which can be after-cross-linked by means of heat, which is based on epoxide and is obtainable by reaction of (i) a bifunctional epoxide of the formula (3) EQU E--X--E (3)
in which
E in each case is a radical having an epoxide function and PA1 X is a divalent organic radical, with (ii) a secondary diamine of the formula (4) ##STR1## in which R.sup.1 and R.sup.2 can be identical or different and are each hydrocarbon radicals, which can be joined to one another to form a ring system, and PA1 Z is a divalent hydrocarbon radical. PA1 A. a polyepoxide; PA1 B. a chain-lengthening agent chosen from compounds according to the formulae 1 and 2; ##STR2## C. if appropriate, a catalyst for the reaction between the polyepoxide and the chain-lengthening agent; and PA1 D. if appropriate, a dihydroxy-hydrocarbon compound, which can also contain halogen substituents, in which R.sup.1, R.sup.2 and R.sup.3 independently of one another each hydrogen or a substituent which does not substantially influence the reaction between the primary amines and epoxide groups and which does not catalyze the reaction between epoxide groups with one another; R.sup.4 is a C.sub.1-20 -alkylene, C.sub.5-20 -cycloalkylene or C.sub.6-20 -arylene group, it being possible for these groups optionally to be substituted by further non-influencing groups; and R.sup.5, independently of one another, are in each case a C.sub.3-20 -secondary or tertiary alkyl, C.sub.5-20 -cycloalkyl or C.sub.6-20 -aryl group, it being possible for these groups optionally to be substituted by further non-influencing groups; with the limitation that at least one of the groups R.sup.1 or two of the groups R.sup.2 and R.sup.3 must not influence the reaction. PA1 (i) the reaction product of PA1 (ii) a dispersing agent in a sufficient amount to disperse the composition in water; PA1 (iii) if appropriate, a solubilizing agent; and PA1 (iv) water; in which R.sup.11 is a linear or branched, unsubstituted or hydroxy-substituted C.sub.4-20 -alkyl group. PA1 (A) a compound which contains at least two 1,2-epoxide groups and which is a reaction product of an epoxide-amine adduct obtained by reaction of PA1 (A1) compounds having on average at least two 1,2-epoxide groups per molecule, if appropriate mixed with monoepoxides, and PA1 (A2) one or more amines chosen from PA1 R.sup.2 and R.sup.3 in each case independently of one another are hydrogen or one of the radicals mentioned under R.sup.1, hydrogen being particularly preferred for R.sup.3, with the proviso that the amino group is not bonded directly to an aromatic radical and, in the case where R.sup.2 and R.sup.3 are hydrogen, the remaining radical R.sup.1 is one of the following substituents ##STR5## in which the radicals R.sup.4 to R.sup.9 in each case independently of one another have the meaning of a branched or unbranched aliphatic, cycloaliphatic, araliphatic or aromatic hydrocarbon radical which has 1 to 30 carbon atoms and is optionally substituted by hydroxyl, alkoxy or halogen groups, and R.sup.1 and R.sup.2 can form an optionally substituted cycloaliphatic ring having up to 8 carbon atoms, in which case R.sup.3 is then a hydrogen atom, and PA1 R.sup.10 is an aliphatic, cycloaliphatic or araliphatic hydrocarbon radical which has 2 to 30 carbon atoms and is optionally substituted by hydroxyl, alkoxy or halogen groups, or an oxyalkylene radical having 1 to 200 oxyalkylene units and PA1 R.sup.11 in each case independently of one another are an aliphatic, cycloaliphatic or araliphatic hydrocarbon radical which has 1-20 carbon atoms and is optionally substituted by hydroxyl, alkoxy or halogen groups, with the proviso that at least one hydrocarbon radical bonded directly to the particular nitrogen atom is a secondary or tertiary radical, and PA1 R.sup.18 is a direct bond, a linear, branched or cyclic, optionally substituted alkylene group or an arylene or heteroarylene group, with the proviso that at least one of the radicals R.sup.14 to R.sup.17 is an alkyl group if R.sup.18 is a direct bond or a linear alkylene group; and R.sup.14 with R.sup.16 or R.sup.18 and the atoms joining them can form a cycloaliphatic, aromatic or heteroaromatic ring, and PA1 (A3) polyfunctional isocyanates which contains at least two isocyanate groups per molecule, the polyvalent radical bonded to the isocyanate groups being chosen from aromatic, linear, branched or cyclic aliphatic and mixed aromatic-aliphatic radicals; PA1 (B) optionally, 1,2-epoxide compounds which differ from those according to (A1) and/or which are unreacted portions of the compounds (A1) from the preparation of the compounds (A); PA1 (C) curing agents; and PA1 (D) optional further additives. PA1 reacting epoxides (A1) with one or more amines (A2) until a predetermined epoxide group content is achieved to prepare an epoxide-amine adduct; PA1 reacting the epoxide-amine adduct with polyfunctional isocyanates (A3) to form epoxy compound (A); and PA1 mixing epoxy compound (A) with optional additional epoxy compounds (B), with curing agents (C) and with optional further additives.
The diglycidyl ether of bisphenol A preferably is employed as the epoxy resin and N,N'-dimethylethylenediamine and N,N'-diethylethylenediamine, for example, preferably are employed as the dialkylalkylenediamines. This epoxy resin is used as an adhesive, for coatings and as a matrix composition.
EP-A 0 496 163 describes a cured epoxy resin comprising the reaction product of:
These chain-lengthened solid epoxy resins are employed, inter alia, for powder coating. They have higher softening points and higher melting points at a higher specific epoxide group content (SEC) (=lower epoxide equivalent weight), when compared with conventionally lengthened epoxy resins. ("Epoxide equivalent weight" in this context denotes the molar mass of the compound in question based on the number of epoxide groups, also called the "EV value". The EV value is the reciprocal of the SEC.) One embodiment relates to the aqueous dispersions of amine-lengthened epoxy resins comprising:
A. a polyepoxide; PA2 B. a chain-lengthening agent corresponding to one of the formulae (1), (2) (see above) and (5) (=formula 17 of EP-A-0,496,163); EQU R.sup.11 --NH.sub.2 (5); PA2 C. if appropriate, a catalyst for the reaction between the polyepoxide and the chain-lengthening agent; and PA2 D. if appropriate, a dihydroxy-hydrocarbon compound, which can also contain halogen substituents; PA2 (A21) sterically hindered monoamines of the formula I ##STR4## in which R.sup.1 is a branched or unbranched aliphatic, cycloaliphatic, araliphatic or aromatic hydrocarbon radical which has 1 to 30 carbon atoms and is optionally substituted by hydroxyl, alkoxy or halogen groups, PA2 (A22) amines of the formula II EQU R.sup.11 --NH--R.sup.10 --NH--R.sup.11 (II) PA2 (A23) diprimary diamines of the formula III ##STR6## in which R.sup.14 to R.sup.17 are hydrogen or an alkyl group having 1 to 8 carbon atoms and
In addition to the amines 1 and 2 already mentioned above as component B, compounds of the formula (17) R.sup.11 --NH.sub.2 can additionally be employed in component (i) B for the epoxy resin dispersed in water. More precise details on the nature of a possible branching of the radical R.sup.11 are not found in the patent specification. For example, as additional compounds of formula (17), n-Hexylamine is employed as the chain-lengthening agent in Example 8, and n-octylamine is employed in Example 12.
The aqueous embodiment of the epoxy resins according to EP-A 0 496 163 comprises complex mixtures in which solid resins are said to be provided as stable dispersions in water. These dispersions are useful, inter alia, as coatings for curing at ambient temperature, in paper latex, in cement dispersions and in other water-containing coatings.
U.S. Pat. No. 4,886,867 describes, inter alia, a method for preparing difunctional epoxy resins of the formula (6) ##STR3## in which R originates from a bisphenol A diglycidyl ether radical, iPr is an isopropyl radical and x is 2 to about 10. The method entails reacting excess epoxy resin with a secondary isopropylamine derivative of a primary polyoxyalkylenedi- or -triamine in the presence of acetone. In this method, the reaction of the amine component with the bisphenol A epoxy resin is critical. To prevent gel formation, a solvent must be added during preparation of the adduct. Suitable solvents are ketones and alcohols, and acetone is particularly preferred. The difunctional epoxy resins can be solid or liquid, depending on the starting material, and, in the cured state, provide a transparent, flexible, rubber-like material. The examples of this patent reveal that the diepoxides based on bisphenol A resin (.RTM.Epon 828) are semi-solid products and those based on .RTM.Eponex 151 (hydrogenated .RTM.Epon 828) are indeed liquid, but have very high viscosities (cf. Table 1 page 9/10).
According to U.S. Pat. No. 4,316,003, an adduct for curing epoxy resins for aqueous systems is obtained by first reacting excess epoxy resin with a primary monoamine in a 1st stage and then reacting the resulting epoxide with an excess of a polyfunctional amine in a 2nd stage. The products of the 1st stage are prepared in the presence of solvents and are further processed directly in the 2nd stage to provide the amine hardener. No statements are made on the storage stability and on any use of stage 1.
Coatings produced according to EP-A 0 675 143, especially in the case of the highly elastic formulations, show a tear propagation resistance. These coatings, however, still are not adequate for many uses.